Loud speaker



LOUD SPEAKER 2 Sheets-Sheet 1 Filed May 25, 1929 //Vl/E/V7'OP E. A. SANDEMAN Wm @M Afro/M51 Dec. 18, 1934. E. K SANDEMAN LOUD S PEAKER 2 Sheets-Sheet 2 Filed May 25, 1929 //\/l EN7O/? E. K SANDEMAN A TTORNE) type.

Patented Dec. 18, 1934 UNITED STATES PATENT OFFICE a I LOUD SPEAKER 7 Edward K; Sandeman, Aldwych, London, England,

assignor to Western Electric Company, Incor- ..jporated, New York, N. Y., a corporation of New York Application May 25, 1929, Serial No. 365,835

In Great Britain August29, 1928 18 Claims.

The invention relates to apparatus for translating electrical vibrations into acoustical vibrations and more particularly to sound generators either of the direct acting type or of the horn A feature of this invention is to provide means for increasing the radiation resistance of a sound generator particularly at low frequencies. In a sound generator such as the loud speakers of the prior art, it is necessary in order to obtain a radiation resistance which is not too low 'to use either a horn of a cumbersome size or a baffle plate which to be efficient must have large dimensions.

It is known to decrease the solid angle into which the diaphragm works from 41r to approximately 271" by means of a battle board and by this means to secure a larger radiation resistance for the low frequencies than would be the case were the baffie board not'present. However, in order to obtain a proper radiationof the low frequencies essential in speech and music, it is necessary to give to said baffie board a large size, and even in ;that case the radiation resistance of a diaphragm associated with such baffle board is rather small. This small radiation results in reducing very much the volume of sound which i a given diaphragm.

Accordingto the invention a ing planes reduce the solid "angle-into which the diaphragm discharges to approximately s emitted from device for translating electrical vibrationsinto sound waves is provided, the said translating device comprising a sound generator located in a corner provided by three planes intersecting one another for instance at right angles so that the said convergtion results.

In'the following the invention is described by way of example with reference to the accompanying drawings in which:

Fig. 1 isa perspective view of a'sound generator according to the invention.

Fig. 2 shows a section through Fig. 1 on a plane through YWV where WV bisects tween X and Z axes.

the angle be- Fig. Bshows an alternative to the arrangement of Fig. 2.

Fig. 4 shows another form of construction.

Figs. 5 and 6 show a further type of construction in which the driving unit is located within a housing, the outer surface of which is adapted to modify the path of the sound waves.

In the example of Fig. 1, a sound generator, comprises a diaphragm 1, which may be of cardboard, papier-mache, impregnated silk, celluloid, 10 bakelized paper, fibre or other suitable material. This diaphragm is supported in a circular hole in a supporting structure sound board (2) for instance of wood, having the shape of an equilateral triangle (hereinafter referred to as the delta piece), by means of an annular piece of material (3), which has a small transverse stiifness for displacements of the diaphragm which may be of the order of of an inch in either direction along its axis. This annular piece may be made of rubber, wash-leather, or other suitable material. The diaphragm is driven in a known manner for example by a coil situated in a radial magnetic field and traversed by audio frequency currents.

- The triangular supporting structure (2) is intended: to be placed in the corner such as of a room where three bounding surfaces meet at right angles, in the manner indicated in Fig. 1. It is there shown situated in the corner formed between two walls A and B and the floor C, but it may equally (and preferably) be placed in a corner formed by two walls and the ceiling of a room. Where unevenness of the walls occurs, as for instance might be caused by the presence of a skirting board or a picture rail, the edges of the wood must be cut away so that a tight joint is maintained between the wood and the wall. This joint may be made good either by the use of felt or baize or by means of aplastermaterial such as putty, clay or plasticine, or by means of builders plaster or other suitable material.

' In Fig. 2 the diaphragm 1 is driven by a coil (4) situated in the radial magnetic field provided by the magnet (5) supported on brackets (6). Suitable means, not shown, may be employed for centering the coil in the air gap.- D is-the diameter of the pot magnet in inches and h is the distance in inches from the plane of the back of the delta piece (2) to the bottom of the magnet.

Fig. 3 shows an alternative method of construction intended to reduce the value of h and also to increase the value of the radius of the 5 Cal Fig. 4 shows a type of construction in which the pot magnet is placed in front of the are phragm, the intention of this form of construetion being to ensure that the initial angle into which the diaphragm operates is not greater than The diaphragm is here in the form-of ayramia with three curved sides abutting on the-three bounding surfaces. In this case radiation occurs trom the side of the diaphragm-nearest the pot magnet.

In Figs. 5 and 6 there is shown a further .embodiment of theinvention in which -a.sound genorator is located ,in a corner provided by three surfaces, which in the case of the figures are three planes intersecting one another at an an gle of substantially 90". In these figures the reference characters Y and V designate similar elements as do the same lettersgin Fig. '1.

Fig. 5 a sectional view taken along the plane YOV .bisecting the angle XOZ shownin :-Fig. .1. The sound generator shown in this embodiment comprises a diaphragm 1 driven by a driving unit 3 of the moving :coil type, the diaphragm 1 is-associa'ted with a-smallhorn 20, thissm'all horn 20 forming part of the sound conduit. The driving unit 3, and the diaphragm 1', are located within a housing 17;v the horn 20 and the casing 17 .may be both of triangular cross section and the bounding surfaces of the :casing- 1'7 are symmetrically arranged with regard :to the three rectangular planes A, B and C of Fig. 1. The casing 17 is carried by the-supporting structure 10 and 11.

In front of the horn and supported'byimember 12 is situated a sound deflecting member '16, the outer surface of which together with the surfaces of the three planes providing the said corner and the outer surface 15 :of saidh'ousing 17 form a sound conduit in whichthe successive areas encountered by a sound wave originating from the diaphragm and propagated along; the soun-dconduit may be made to vary accordingto the exponential law or according to any other suitable law as may be desired.

For determining the shape of thesurfaces115 and 16, the well known method-oi descriptive geometry may be used. It should be-remarked that the methods of descriptive geometry en able one to determine the outer surfaces of ,the housing 17 and of the deflecting member 16 so that the sectional area of the soundconduitprovided between the three rectangular planes and the bodies 17 and 16 vary according to any given law. 1

The surface of the mouth opening -of the horn, provided by the arrangementof- Figs. 5 and 6 on the plane KG is that of the base of a triangular pyramid, the other sides of which are formed by the floorOG together with the-two walls.

The known principles of horn design may be used for determining the successive cross; sectional area of the sound conduit. It will-be seen that sound conduits as shown in the accompanye (1) A=A0ewhere As is the areaof the initial mouths openin'g', representslength measured along the sound path of the horn in inches, and e is the well known constant e=2.71828 Taking the lines OY and 0V ofTFig. 5 as reference axes, the

lengths such as G" K I, G H, etc. will bechosen so that the areas of the flares of which K" I, G" H, etc., are the projections intercepted between the three mutuall-yrectangular planes A, B and C and the outer surface of the casing 17 as shown in Fig. 5, vary according to ,the given law (1). "This will determine the position of points I, H, I, H, etc., and thereby the outer shape of the housing 17. The surface of the deflecting member 16 will be determined in asimilar manner.

The axis 0T of the sound generator may be more or less inclined on; the plane of trace ,OV. In thecase of Fig. 5' the axis OT forms an angle withOViof about In Fig. 6 there is shown an end view of the arrangement of Fig. 5, the deflecting member is shown in 6 and the housing in 5. The triangle FF,8,--.9' is an aperture through which the driving unit and diaphragm may be introduced and is normally closed bymeans of alid 13,- this lid being maintained fixed by bolts 14.

'I'heaperture 7, 8, 9 may-be left open or the lid may be provided with a hub' or opening (the boundary of which is indicated by dotted line 18) of-sui-table size, This results in a relative increase the reproduction eflicieney of the loud speaker for certain frequencies. I H some cases the small horn 20 may be dispensed with, the diaphragm 1 being placed directlyfiin front of the deflecting member 16,- in this case it is also possible to shape the outer surface of -the housing 17 so that the diaphragm 1, the housing 17, the deflecting member 16, and the three bounding surfaces (A, Band C in Fig. 1) co-operate to forma horn of large dimensions.

What is claimed is:

1. A sound generator comprising a diaphragm, means for driving said diaphragm, a casing for said driving means, said diaphragm being supported by said casing, and a deflecting member adapted to .be readily located in a corner provided by t'hree rectangular planes, thesurface of the deflecting member looking toward said diaphr'agm, together with the surface of said casing beingls'o shaped-that no steep change is introduced thereby in the propagation of the sound wavesgenerated by said diaphragm.

s2. A loud speaker comprising a diaphragm, means for driving the diaphragm, means for supporting said diaphragm and driving means, and a deflecting member adapted to be positioned substantially at the vertex of a corner formed by at least three surfaces meeting each other, and a horn of relatively small dimensions, the mouth of said horn being directed toward said deflecting member, and the surface of said deflecting member shaped with regard to the outer surface of said horn and of the faces of said corner so that the cross sectional areas contained between said surfaces are varied gradually whereby no steep change is introduced thereby in the propagation of the sound waves along and out of said horn.

3. A sound generator comprising a deflecting member adapted to be placed in the vertex of the corner of an enclosure formed by at least three plane surfaces meeting each other at right angles, a casing, and a horn housed in said casing, the mouth of said horn being directed toward said deflecting member, the surface of said deflecting member looking toward the mouth of the horn, tapering gradually, so that no steep change is introduced thereby in the propagation of sound waves.

4. A loud speaker comprising a diaphragm, means for driving said diaphragm, and a casing for said diaphragm and driving means, said casing being adapted to be placed in the corner of a room with the diaphragm facing the vertex of the corner, the outer surface of said casing proportioned with regard to the surfaces providing said corner so that the cross-sectional areas contained between said surfaces vary gradually so that no steep change is introduced thereby in the propagation of sound waves along the sound directing surfaces formed by the surface of said casing and by the surfaces providing said corner.

5. An acoustic device comprising a diaphragm, means for driving said diaphragm, and a triangular shaped soundboard to be positioned in front of the meeting point of three plane surfaces in rectangular relationship with one another, the diaphragm being secured to said sound board.

6. A large direct acting pyramidal shaped diaphragm, and means for driving said diaphragm, said diaphragm being adapted to be tpositioned in a sound passage formed by at least .three plane surfaces, meeting each other at an angle of 90 the base of said diaphragm being in close proximity to said planes.

7. An acoustic device comprising a diaphragm, means for driving said diaphragm, and a sound board adapted to fit in a corner defined by a plurality of converging plane surfaces, the diaphragm being secured to said sound board.

8. An acoustic device comprising a diaphragm, means for driving said diaphragm, and a sound board to which said diaphragm is secured, adapted to be positioned in front of the meeting point of a plurality of converging surfaces, the peripheral edge of said sound board being in contact with said surfaces.

9. An acoustic device comprising a diaphragm, means for driving'said diaphragm, and a sound board to which said diaphragm is secured, said sound board to be positioned in front of the meeting point of a plurality of converging plane surfaces, the peripheral edge of said sound board forming a tight joint with said surfaces.

10. An acoustic device to be positioned in a corner, constituted by the convergence of three plane surfaces, comprising a triangular sound board, whose periphery bears against said plane surfaces.

11. An acoustic device comprising a diaphragm, means for driving said diaphragm, a horn of small dimensions, a casing surrounding said horn and diaphragm, and a sound deflecting member, said member and easing being positionable at the apex portion of a corner constituted by a plurality of converging plane surfaces, said member having its surface directed toward, but in spaced relation to, the mouth of said horn, said horn, casing, sound deflecting member and converging surfaces defining a sound passageway whose cross sectional area varies logarithmically as the distance from the throat of the horn increases.

12. In an acoustic device to be positioned in a corner constituted by a plurality of converging plane surfaces and comprising a diaphragm, means for driving said diaphragm, and a casing enclosing said diaphragm and driving means, and having a reentrant portion constituting a horn into which said diaphragm discharges and an opening therein whereby the rear surface of the diaphragm is open to the atmosphere outside the casing, said casing being positionable in spaced relation to the corner so that the surfaces thereof constitute an extension of the born.

13. A sound translating device to be positioned in a corner constituted by a plurality of converging walls, comprising a pyramidal shaped diaphragm having a plurality of curved sides, and actuating means for said diaphragm, said diaphragm being positionable in said corner, each curved side abutting on one converging wall.

14. An acoustic device positionable in a corner consisting of a plurality of converging surfaces, comprising a supporting member having an aperture therein, a diaphragm having its rim mounted adjacent the edge of said aperture, and diaphragm actuating means mounted on said member, said member being positionable in said corner and having a plurality of edge portions at least two of which engage at least two converging surfaces.

15. An acoustic device comprising a diaphragm, means for driving the diaphragm, a casing enclosing the diaphragm and driving means, said casing having a reentrant portion constituting a horn into which the diaphragm discharges, an opening behind said diaphragm, and a removable cover member closing said opening.

16. An acoustic device comprising a supporting member having an aperture therein, a diaphragm having its rim mounted adjacent the edge of said aperture, and diaphragm actuating means mounted on said member and within said aperture, said member being positionable in a corner defined by at least two converging surfaces and having a plurality of edge portions at least two of which engage at least two converging surfaces.

17. An acoustic device comprising a supporting structure having a substantially triangular periphery to be placed in acorner defined by three converging surfaces, said structure having an aperture therein, a diaphragm for radiating sound waves directly into the air and having a frustoconically shaped portion, the circumference of whose larger base is adjacent the defining edge of said aperture, and means attached to said diaphragm for communicating sound wave energy impulses thereto.

18. An acoustic device comprising a diaphragm to radiate sound waves directly into the air, means for actuating said diaphragm, and a planar supporting structure having an aperture with which the diaphragm is coaxial, and being triangular in shape to fit against three converging surfaces.

EDWARD K. SANDEMAN. 

